Only 40 percent of dams in Japan can pre-emptively release their reservoirs' water prior to heavy rains to mitigate flood risks, a Kyodo News survey showed Monday.

The lack of the "pre-release" function has forced some dam operators to enact emergency discharge only after water levels approached their limit in recent typhoons and other rain disasters. Some people died due to swollen rivers caused by such a release in the 2018 torrential rain in western Japan.

The government has been calling for dam operators to prepare the function for strategic release and actively manage water levels. But improvement work will likely cause various challenges including costs.

The survey, conducted last month, found that 246 out of 559 dams operated by 57 organizations throughout the country are able to pre-release water prior to forecast rainfall.

Forty-five bodies saying they have difficulty doing so cited reasons including the structures of existing dams, such as lacking discharge gates or having discharge conduits with weak drainage capacity.

One of the respondents said that if they pre-release water but have no rain, the resulting water shortage entails risks to farmers and water utility companies and negatively impacts society at large.

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